A technology of recording and reproducing information on/from the information recording medium using laser light has already achieved a practical use of an optical disk apparatus etc. As one method for a rewritable optical disk apparatus, there is a phase change type optical disk that utilizes a reversible phase change between crystalline and amorphous states. In order to obtain these two states, light of a high power (recording power) is irradiated on the recording medium, which is heated over a melting point and then is quenched quickly to convert to the amorphous state; light of an intermediate power (erasing power) lying between the above-mentioned high power and a reproducing power is irradiated on the recording medium, which is heated up to the crystallizing temperature and is cooled gradually to convert to a crystalline state. Therefore, overwriting can be performed with light of a single laser.
Conventionally, in the recording method based on the above-mentioned light irradiating method, as described in U.S. Pat. Nos. 5,490,126, 5,636,194, and the DVD-RAM JIS Standard (120 mm DVD Rewritable Disk JIS X 6243/P86, Attachment H, Definition of Writing Pulse), at least three power levels consisting of the recording power (high power level) for overwriting, the erasing power (medium power level), and the reproducing power for reducing thermal interference (low power level) are used; and the recording mark is classified into three kinds, namely a first part, an intermediate part, and a last part, and, an information is recorded by a recording pulse whose effective length (length from a rise of the first pulse to a fall of the last pulse) corresponds to the length of data to be recorded (recording code length). Further, this recording method adopts a recording method where, in the first part and in the last part, light of the above-mentioned recording power is irradiated for a constant period of time; in the intermediate part, light of the recording power and light of a power smaller than the recording power (erasing power) are switched alternately and irradiated so that the cycle thus created becomes smaller than the above-mentioned constant period of time; and after the light of the recording power irradiated in the last part, light of a power (reproducing power) lower than the erasing power is irradiated for a constant period of time to decrease the thermal interference.